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Panasonic 2010 plasma: Floating blacks

305K views 2K replies 317 participants last post by  Majcric 
#1 ·
Floating Blacks:


I purchased a TC50G20 from Best Buy on March 6th. I also purchased their new Panasonic Blue Ray player. The THX setting mode out of the box is gorgeous. But wait, there's more.. The first blue ray I viewed was the Matrix, 10th Anniversary Edition. I loved this G20 until I saw the gamma levels change 4 times during the scene when Trinity rolls down the stairway and aims her guns up at the window. I also noticed the same "lightening and darkening" of the screen while watching a scene from Pirates 3 between on the ship at night.


I can rewind and watch it over again and can see it every time. This drives me nuts. What's frustrating is that the gamma/brightness shift is not simultaneous with the scene changing: the set takes a moment to adjust to the frame in the movie. This occurs even with the CATS setting off. A darker scene in the movie with more blacks causes the set to adjust and the blacks become "darker" a few moments later. It is so obvious that I am not able to watch blue rays in the dark at this time, and I'm even considering returning the set. Call me picky, fine. But I'm not happy about this issue. After tinkering, I realized that the shift is less evident when the set is watched on the "dark" setting found in the advanced menu. Also, on the "custom mode" set up, I can set the gamma to 2.6 on the pro menu and eliminate the problem. The downside with both these settings is I lose grays and contrast. No one I've spoken with at Panasonic even knows the difference between infinite black and infinite black pro, let alone what floating blacks are, really?


My question: Is there any way to fix or lesson this change? What causes floating blacks? Is this a power issue? Is it a tech issue? What alternative do I have other than the new Panasonic 2010 Plasma line to get great blacks? Will the v-series have this issue with the infinite black "pro" panel? These are my questions. Yes, I have adjusted the brightness multiple times and no fix. Any help will be appreciated.
 
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#27 ·

Quote:
Originally Posted by roobieroo /forum/post/18347559


I absolutely agree with you on this. People need to remember that this does not include message boards. If you really want this addressed then you need to call Panasonic and make them aware of how you feel. Just because someone else posted that they've talked to Panasonic doesn't mean you don't need to call them yourself. The more calls they get the more likely they are to do something about it.

"The TV is working as designed. There is nothing wrong with it and the Picture is beautiful. Bye Bye" - Panasonic standard answer to everything.
 
#28 ·

Quote:
Originally Posted by xrox /forum/post/18348036


How does the floating black level manifest itself? In other words does the black level go up (get brighter) when the APL is lowered?

Just personal interest but if someone could try and describe how the floating blacks present themselves with regards to APL that would be great



BTW, APL is Average Picture Level which can be equated to how bright the overall screen is or % of screen at full white or average brightness....etc


So if a bright scene switches to a dark scene....what does the black level do?


If a dark scene switches to a bright scene what does the black level do?


Cheers
 
#29 ·
Try this; find a very dark scene and a very long. Wait until the subtitles shows, or force the subtitles on and off, of the picture. If the picture gets brighter when the subtitles comes then you will instantly know what to look for.


Loop that scene and play with the brigtness settings. Often the "effect" shows when brightness is set lower. Sometimes the fluctuation stop if you raise the brightness.
 
#30 ·

Quote:
Originally Posted by surap /forum/post/18356772


Try this; find a very dark scene and a very long. Wait until the subtitles shows, or force the subtitles on and off, of the picture. If the picture gets brighter when the subtitles comes then you will instantly know what to look for.


Loop that scene and play with the brigtness settings. Often the "effect" shows when brightness is set lower. Sometimes the fluctuation stop if you raise the brightness.

Not sure if you were responding to my post or not. I should have stated that I don't want to see the effect (as I don't have a Panasonic PDP). I just need a simple description of the direction of black level shift (up or down) with respect to APL so that I can cross reference the information from the patent I mentioned to the information here.


Cheers
 
#31 ·

Quote:
Originally Posted by xrox /forum/post/18356444


Just personal interest but if someone could try and describe how the floating blacks present themselves with regards to APL that would be great



BTW, APL is Average Picture Level which can be equated to how bright the overall screen is or % of screen at full white or average brightness....etc


So if a bright scene switches to a dark scene....what does the black level do?


If a dark scene switches to a bright scene what does the black level do?


Cheers

The black levels fluxuate on mid/low APL scenes. I have not seen floating blacks during high APL scenes.
 
#32 ·

Quote:
Originally Posted by D-Nice /forum/post/18357853


The black levels fluxuate on mid/low APL scenes. I have not seen floating blacks during high APL scenes.

Thanks, but is there a predictable direction (up or down) of the black level shift with APL or does it seem random?


Cheers
 
#33 ·

Quote:
Originally Posted by xrox /forum/post/18357917


Thanks, but is there a predictable direction (up or down) of the black level shift with APL or does it seem random?


Cheers

Random, but repeatable
 
#34 ·

Quote:
Originally Posted by Rick1000 /forum/post/18347057


Here is a post describing Panasonic floating blacks:



05-15-09, 02:26 PM #35 | Link

PENDRAG0ON

AVS Special Member





Considering how floating blacks isn't caused by the technology, but rather a processing algorithm, I doubt that he considers it a deal breaker, especially since it isn't an issue on Pioneer sets. (Sony LCDs and Samsung LED LCDs have this problem as well (though Sony fixed it on their 09 models with a firmware update) Panasonic plasma sets' "Real Black Drive" is what you should blame for their floating blacks, and it is something that they should dump or at least let us turn it off. (as should all TV sets that use this lousy feature) I haven't checked to see if their G series has this or not, but I will be sure to do so once I pick one up within the next week.


Something to remember though, if we don't complain about problems with these TV sets, then they won't fix said problems.

Not my best post on the subject, but it does get the idea across. This was eliminated in the 2009 1080p Panasonic models that I had, so it shouldn't be there on the 2010 models unless they added it back to help cover up the rising black levels.


The best way to tell if it is happening is to watch a black bar movie and see if the black bars are dimming and brightening as well as the content. With the old Panasonic models, the black bars would fluctuate noticably on most black bar movies, the 2009 models didn't have any fluctuation unless the black levels rose while you were watching it.
 
#36 ·

Quote:
Originally Posted by D-Nice /forum/post/18357930


Random, but repeatable

Thanks, that seems to fit with the 20090021452 patent applicaton. It states that the black level will shift at 6% APL (gets darker below 6% and brighter above 6%). Also says that if a hysteresis characteristic is applied there will be two thresholds at 5% and 7%.


These particular APL thresholds may create a very random effect as average brightness will be difficult to differentiate in many of the scenes (ie - credits, mostly dark scenes with bright spots...etc)
 
#37 ·

Quote:
Originally Posted by barrist /forum/post/18358104


I notice this (if i'm understanding the phenomenon correctly) sometimes on my Pio 4270. Anyone know if this is the same thing? if so, its not that noticeable/troublesome to me usually.

Are you using Pure Cinema Advance?
 
#40 ·

Quote:
Originally Posted by skoor /forum/post/18358270


So what is the patent's claimed advantage? Did I miss it in an earlier post? Surely they did for some other supposedly advantage. Not just to bug us.

Very sneaky patent IMO
My interpretation is this:


The panels 'normal' or 'natural' black level is the higher black level seen above 6% APL. This black level allows for stable high speed operation. When there is below 6% APL the panel switches to a lower black level to maximize contrast to the viewer at the expense of driving stability.


So, stated simply. IMO the advantage is to increase contrast when a lot of black is on the screen.


Note: According to this patent it sure does seem that Panasonic Plasmas 'natural' black level is either hidden in high APL scenes (floating blacks) or deferred (rising black levels).
 
#42 ·

Quote:
Originally Posted by xrox /forum/post/18356841


Not sure if you were responding to my post or not. I should have stated that I don't want to see the effect (as I don't have a Panasonic PDP). I just need a simple description of the direction of black level shift (up or down) with respect to APL so that I can cross reference the information from the patent I mentioned to the information here.


Cheers

Ooops, sorry. No it was meant as a test...
 
#43 ·

Quote:
Originally Posted by xrox /forum/post/18359215


Very sneaky patent IMO
My interpretation is this:


The panels 'normal' or 'natural' black level is the higher black level seen above 6% APL. This black level allows for stable high speed operation. When there is below 6% APL the panel switches to a lower black level to maximize contrast to the viewer at the expense of driving stability.


So, stated simply. IMO the advantage is to increase contrast when a lot of black is on the screen.


Note: According to this patent it sure does seem that Panasonic Plasmas 'natural' black level is either hidden in high APL scenes (floating blacks) or deferred (rising black levels).

I haven't reviewed the patent, but based on your description, I can make a simple guess as to the motivation for the floating blacks method. Maybe you can tell me if this is close to the mark or not ...


To make things simple, lets assume that the drive electronics can drive any plasma cell with digital values ranging from 255 (max brightness) to 0 (min brightness). This range of 256 drive values represents the full dynamic range of the cell. One issue that would exist is it takes non-zero time to charge a cell from 0 to 255, or to discharge the cell from 255 to 0. In other words, the larger the voltage difference from one pixel state to the next, the longer it takes to get to the next state (i.e. it takes time to raise/lower the voltage on a capacitive load). This charge/discharge time affects how fast the display can run.


To see what that would mean in practice, assume for a moment that Panasonic's panels are capable of really dark blacks (e.g. dynamic range of 0 to 255) and that Samsung's panels aren't quite as nice in that regard and have relatively brighter blacks (e.g. dynamic range of only 32 to 255). If both the Panny and Samsung drive circuits were identical, this means the Samsung panel would run faster because the voltage change from darkest to brightest wouldn't take as long (if/when the need occurs in a frame change). The Panny on the other hand would be slower but have darker blacks. In this regard, there is a tradeoff between panel speed and dynamic range.


Taking my guess one step further, maybe Panasonic feels that a dynamic range for any particular APL level of 255-32+1=224 is good enough - even if the plasma cells can handle 0 to 255. This would be beneficial because the panel could run more reliably at a faster speed (again, smaller voltage swings means faster charge/discharge cycles). But maybe the clever engineers @Panny decided to employ a twist ... during high APL, plasma cells would be driven between 32 to 255, and during low APL, 0 to 223. The two APL regimes have the same range (so the display runs at the same fast speed) but the low APL regime appears to have very dark blacks (0 compared to 255 as opposed to 32 compared to 255). That seems like a big win except the absolute black levels in each APL range are different. So the circuit & firmware responsible for the range switching should be designed carefully to avoid the perception of floating blacks.


Another potential advantage of this method should be that power consumption would be lower by not using the full dynamic range of the cell. Given California's new HDTV power regulations for 2011, this would help keep Panny in a large market.


Anyways, this is just a guess, but we have exactly these same issues in my line of work (design of solid-state memories). Your use of the term "drive stability" made me think of this analogy.


Best.
 
#44 ·

Quote:
Originally Posted by D-Nice /forum/post/18357853


The black levels fluxuate on mid/low APL scenes. I have not seen floating blacks during high APL scenes.

I had a 75u that only shifted during high APL scenes, but my G20 does like you mentioned above. I've tried to lower my brightness on both THX and Custom modes but it seems to make little difference. Neither does the AGC control or Gamma control.


You said you were able to adjust it out of your set, is it possible that some sets may be affected more than others?
 
#45 ·

Quote:
Originally Posted by skoor /forum/post/18360480


What I have stated to notice is not so much the grey bars on films or floating blacks,but that apparently no analog/scanned films really have that deep of black levels native to the source. Certainly so far most are not even close to the black bars for any source. And one of the worst was 2001 BR. God awful and on a Kuro too.


I vaguely remember from my 35mm slides film days noting that I never got true blacks on the screen. If I flashed up a totally unexposed slide, it glowed. And they use to rate films DMax. So even film, which is still way over 90% of most BR sources today can not really do a perfect black.


Are we chasing some holy grail by just looking a grey bars? It is a good test of the set, of course, and you do really want a perfect black, if 0 IRE. But if most of our sources today don't have it to show off our new digital set.


Of course, a totally digital source, like CGI or animation, could have perfect blacks. But if that source, I have found grey star fields and night skies even on an Kuro 101. Just seems they know people would not expect it. Hey, Panasonic CSR, my picture looks too black! What is wrong? Oh, it is featuere- for once. LOL.

I have come across several HDNet programs that have elevated blacks in the source as well. Typically on my PDP (141 monitor) to reach MLL I need to drop the brightness to -2. However, with these HDNet programs I need to drop it to -20+ at times. I think D-Nice called this phenomenon 'black pedestal' or something along those lines.


Cheers
 
#46 ·

Quote:
Originally Posted by hydrogin /forum/post/18361266


I haven't reviewed the patent, but based on your description, I can make a simple guess as to the motivation for the floating blacks method. Maybe you can tell me if this is close to the mark or not


To make things simple, lets assume that the drive electronics can drive any plasma cell with digital values ranging from 255 (max brightness) to 0 (min brightness). This range of 256 drive values represents the full dynamic range of the cell. One issue that would exist is it takes non-zero time to charge a cell from 0 to 255, or to discharge the cell from 255 to 0. In other words, the larger the voltage difference from one pixel state to the next, the longer it takes to get to the next state (i.e. it takes time to raise/lower the voltage on a capacitive load). This charge/discharge time affects how fast the display can run.

Your on the right track by considering time. However, PDPs voltage remains relatively constant throughout the 255 levels. It uses PWM (varies the "time-on") to create different gray levels. Because PDP relies so heavily on time, anything that limits time will limit both the number of gray levels and the peak brightness of the PDP. Some parameters that limit time in PDP operation:


1 - resolution (more pixels to address means less time to emit light)

2 - discharge delay (time lapse from voltage application to actual discharge)

3 - Length of initialization period (initialization does not contribute to gray level and thus eats up time)

4 - # of initialization periods


Reduction of #2-4 above opens up a lot of time which enables improvements in brightness and # of gray levels. Specifically, reduction of #2 allows for high speed addressing and reduction of #3-4 creates lower black level as well as enabling higher brightness and more gray levels.


In the case of floating blacks only 1 intialization period is used below 6% APL and 2 intialization periods are used above 6%. So you are correct that "time" is saved by using the floating black system. However, I still see the main advantage as increasing contrast (better blacks) at low APL.

Quote:
Originally Posted by hydrogin /forum/post/18361266


To see what that would mean in practice, assume for a moment that Panasonic's panels are capable of really dark blacks (e.g. dynamic range of 0 to 255) and that Samsung's panels aren't quite as nice in that regard and have relatively brighter blacks (e.g. dynamic range of only 32 to 255). If both the Panny and Samsung drive circuits were identical, this means the Samsung panel would run faster because the voltage change from darkest to brightest wouldn't take as long (if/when the need occurs in a frame change). The Panny on the other hand would be slower but have darker blacks. In this regard, there is a tradeoff between panel speed and dynamic range.

MLL (produced by the initialization period) is not part of the 0-255. MLL can be raised or lowered via voltage changes or # of periods without changing the 0-255. In other words MLL is not a gray level and is not intended to be part of the signal. It is unwanted background light.

Quote:
Originally Posted by hydrogin /forum/post/18361266


IAnother potential advantage of this method should be that power consumption would be lower

Good thinking, when only 1 initialization period is used there should be a small power savings.



Cheers
 
#47 ·

Quote:
Originally Posted by xrox /forum/post/18362165


Your on the right track by considering time ...

I think you're being too generous



Its clear to me now a PDP only resembles a computer memory in that there is row/column addressing. I'd like to learn more about how PDP's work, especially the drive process (sort of like the process of writing to a memory). I found this nice set of slides:

http://www.docstoc.com/docs/24683452...anel-Principle


But there is no text so it leaves one guessing. Are you aware of any similar resources I could study? I suspect a lot of what I want to understand are covered in slides 1-21. If I can understand the timing diagram in slide 21, I should have a foundation to move on to the subfield drive topic, etc.


And BTW, it sounds like initialization is similar to pre-charge in a dynamic RAM where prior to writing, the memory cell spends some time "getting ready" to be written to ( a capacitor is being charged). Perhaps initialization is getting rid of charge from a previous cycle in preparation for taking on a new value in the next cycle ... but that's just a guess.
 
#48 ·

Quote:
Originally Posted by hydrogin /forum/post/18368021


Its clear to me now a PDP only resembles a computer memory in that there is row/column addressing. I'd like to learn more about how PDP's work, especially the drive process (sort of like the process of writing to a memory).

Yes there are two row electrodes and one column electrode. There is no TFT control in PDPs. Control of the pixel is achieved through dielectric memory charge (wall charge).

Quote:
Originally Posted by hydrogin /forum/post/18368021


If I can understand the timing diagram in slide 21, I should have a foundation to move on to the subfield drive topic, etc.

Slide 21 shows the typical cycle the PDP goes through to generate a single subfield. The example they give is a very old conventional style where each and every subfield contains an initialization step that wipes all charge from every sub-pixel on the panel. Then to write image data, each row of sub-pixels is addressed and individual sub-pixels are set into an "on" or "off" state by creating wall charge only in the cells to be "on" and not creating wall charge in the cells to be "off". Once this is achieved the entire panel is sent AC voltage pulses and only the cells previously set in the "on" state will emit light. It then repeats this cycle about 8-10 times per frame with each sustain cycle having different amount of AC pulses to create PWM.


Check out this post on the Panasonic rising black thread:
http://www.avsforum.com/avs-vb/showt...3#post17831713

Quote:
Originally Posted by hydrogin /forum/post/18368021


And BTW, it sounds like initialization is similar to pre-charge in a dynamic RAM where prior to writing, the memory cell spends some time "getting ready" to be written to ( a capacitor is being charged). Perhaps initialization is getting rid of charge from a previous cycle in preparation for taking on a new value in the next cycle ... but that's just a guess.

In the case described in the pdf you are exactly right. In general the initialization step (also called reset step) serves to equalize the wall charge in every pixel (in this case it means erasing all wall charge to zero) to prepare the array to be written with image data. The 2nd important reason for the initialization step is to generate seed electrons into the discharge space (called priming) which enables the gas to be discharge quickly when voltage is applied in the write step and sustain step.
 
#49 ·

Quote:
Originally Posted by xrox /forum/post/18369105


The 2nd important reason for the initialization step is to generate seed electrons into the discharge space (called priming) which enables the gas to be discharge quickly when voltage is applied in the write step and sustain step.

I didn't realize how important that is until I read your other post more than a few times.


At first I couldn't understand why shorter initializations result in lower black levels than longer initializations. I understood zeroing out the voltage across the cell by bleeding out charge from the subpixel must be a necessary step (so you're always starting from a known state). But I thought the more time spent doing this, the "better" the reset would be. Then I remembered your last sentence above. If a longer initialization also means more time priming, then more seed electrons are going to be introduced. I'm guessing more seed electrons will make it easier/quicker to increase current across the subpixel later on. But maybe this will also create more electrons that can be excited to create phosphor-knocking UV photons? In which case the black level might not be as low as it would have been had a shorter initialization (and slower "turn on") been used? I do remember the PWM signal in the sustain phase is responsible for establishing grey level, but that must be on top of a DC level established by the seed electrons?


I would appreciate knowing what is happening from a gas perspective in the three phases. Again, I'm somewhat unsure and guessing again:


Initialization - Apply voltages across subpixel to bleed out charge. Then apply voltages to inject "seed" electrons and produce +/- charges on opposite walls. Gas is now a low-energy plasma with ionized atoms and electrons? Or perhaps the gas isn't a plasma yet, we've only managed to inject/tunnel some electrons across the dielectric barriers?


Address - Increase voltages and current across subpixel, gas is presently a plasma, introduce more carriers into the plasma until electrons jump their valence shells. Electrons now produce UV photons upon returning to lower energy states. UV photons strike phosphors and emit visible photons.


Sustain - Continue applying voltage (at lower level?) to continue electron excitation. I'm not sure why there are multiple sustain cycles within a single subfield cycle. Could this be some sort of power-saving step given that glowing has a some kind of inertia (glows for awhile, then decays)?


Finally, I was curious in your other thread, you say as the panel ages, the voltage needed to initialize must increase. Is this due to some fatiguing mechanism in the dielectric?


Hopefully after all of this, I will have a big picture and understand how the "floating black level" issue fits in.


Best
 
#50 ·

Quote:
Originally Posted by hydrogin /forum/post/0


I'm guessing more seed electrons will make it easier/quicker to increase current across the subpixel later on?

Yes, well more accurately, the presence of seed electrons reduces the discharge delay. Ionization of the gas becomes easier (less voltage required) and quicker (less delay between voltage application and ionization).

Quote:
Originally Posted by hydrogin /forum/post/0


But maybe this will also create more electrons that can be excited to create phosphor-knocking UV photons In which case the black level might not be as low as it would have been had a shorter initialization (and slower "turn on") been used?

The seed electrons are created via a secondary electron effect. The top two electrodes are coated in MgO which has a very high secondary electron coefficient in Xenon/Neon. When the cell is discharged, high energy ions impact the MgO and electrons are ejected into the discharge space. The black level is visible because during the initialization step the gas is discharged (ionized) creating UV radiation. The strength of this discharge determines the brightness of the black level.


Now, if priming (seed electrons) is very efficient and long lasting then there is less need to prime and thus the black level can be reduced by lowering the voltage or by reducing the number of initialization steps per frame.

Quote:
Originally Posted by hydrogin /forum/post/0


I do remember the PWM signal in the sustain phase is responsible for establishing grey level, but that must be on top of a DC level established by the seed electrons?

Yes, but if there is no image data sent to a pixel, there is no PWM, but the pixel still must undergo initialization to keep up the priming. This is why you see a black level MLL no matter what is on the screen.

Quote:
Originally Posted by hydrogin /forum/post/0


Initialization - Apply voltages across subpixel to bleed out charge. Then apply voltages to inject "seed" electrons and produce +/- charges on opposite walls. Gas is now a low-energy plasma with ionized atoms and electrons? Or perhaps the gas isn't a plasma yet, we've only managed to inject/tunnel some electrons across the dielectric barriers?


Address - Increase voltages and current across subpixel, gas is presently a plasma, introduce more carriers into the plasma until electrons jump their valence shells. Electrons now produce UV photons upon returning to lower energy states. UV photons strike phosphors and emit visible photons.


Sustain - Continue applying voltage (at lower level?) to continue electron excitation. I'm not sure why there are multiple sustain cycles within a single subfield cycle. Could this be some sort of power-saving step given that glowing has a some kind of inertia (glows for awhile, then decays)?

The initialization is usually a ramp pulse that creates a small discharge (ionization) in the townsend region. This charges/discharges the dielectrics and at the same time generates secondary electrons from MgO as mentioned above.


The Address step selectively discharges (ionizes) to create enough wall charge for the sustain step.


The sustain step applies a AC pulse train because each pulse phase creates a discharge followed by quenching and then reverses polarity and repeats. The longer the AC pulse is applied the more discharges occur and the brighter the light emitted.

Quote:
Originally Posted by hydrogin /forum/post/0


Finally, I was curious in your other thread, you say as the panel ages, the voltage needed to initialize must increase. Is this due to some fatiguing mechanism in the dielectric?

They do not explain it in the patent. However, I speculate that the MgO material is sputtered and deposited onto the phosphor in a form that is less electrically active (lower secondary electron efficiency). This will increase the voltage required to discharge the gas, especially in the initialization step.


BTW, I love talking about this stuff so thanks



Cheers
 
#51 ·
I finally spoke with a knowledgeable tech at Panasonic today about the floating black issue. He said it IS in fact an underlying energy star POWER issue on certain models in the 2010 series: S2, U2, C2, I believe were their names. However, he said the G20 and VT20 should NOT be affected by this issue. I don't know enough about "seeding" and "electron photon disruption" and all the other things recently discussed on this thread to talk more about the issue. I just told him I thought it might have to do with needing more power to switch between light scenes and the darker blacks. He says it has been an issue in the past and it was a power issue then too.


He is taking my complaint to engineering to see if anything can be done (firmware update, etc). What disturbed me is that he said right now I am the ONLY one who has called Panasonic about this issue with a G20 set. He seems to think this never happens with a G20. I straight up don't believe that. Dozens of people are whining about this on here. Call Panasonic!!
 
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